Conventionally known is the wireless power transmission system which transmits electric power from a primary power transmission coil provided on the power transmission side to a secondary power reception coil provided on the power reception side such as an electronic device and a vehicle. Owing to the absence of any exposed contact members, the wireless power transmission requires no special water proofing arrangement, and is free from the problems of the failures and degradations of the contact members. The primary power transmission coil and the secondary power reception coil that are contained in the electronic device or the like typically consisted of coil windings wound around cores or bobbins.
In a typical wireless power transmission system, the utility power is converted into high frequency AC power by using a high frequency converter circuit before being fed to the primary power transmission coil, and a high frequency AC magnetic flux at the frequency of 60 to 600 kHz is created in the primary power transmission coil. By means of electromagnetic induction, AC power is induced in the secondary power reception coil provided in the electronic device on the secondary power receiving side, and this power is rectified by a rectifying/smoothing circuit on the secondary power receiving side before being supplied to a rechargeable battery.
Conventionally, when a rechargeable battery of an electronic device is to be recharged by using a power transmission device, the electronic device is placed on the power transmission device. The power transmission efficiency is strongly influenced by the relative position between the electronic device and the power transmission device. If the two parts are not properly aligned, the transmission efficiency sharply drops. When a plurality of electronic devices are to be placed on a single power transmission device at the same time, it is known to assign different priorities to the different electronic devices and to recharge the batteries of different electronic devices on a time sharing basis.
As such a known technology, Patent Document 1 discloses a recharging table including a case having an upper plate to place a battery-incorporated device thereon, a position detecting control unit for detecting the position of the battery-incorporated device, a power source coil (primary power transmission coil) and an actuator for moving the power source coil to the proximity of the induction coil (secondary power reception coil) of the battery-incorporated device.
Patent Document 2 discloses a recharger including a plurality of recharger units each configured to recharge a battery-incorporated device placed in the corresponding recharging area in a contactless manner, a priority assigning unit for assigning different priorities of recharging to the battery-incorporated devices, and a control unit for controlling the supply of electric current to the battery-incorporated devices, wherein the control unit determines the distribution of electric current to the different recharger units from the given amount of available electric current according to the priorities assigned by the priority assigning unit. The recharger is configured to preferentially recharge the battery-incorporated devices assigned with higher priorities when recharging the battery-incorporated devices in a contactless manner.